Plate heat exchanger

ABSTRACT

In a plate heat exchanger having a welded plate pair comprising first and second plates (2, 4) which are welded together at a contact region (19), a by-pass area (22) is defined between the plates on the inboard side of the contact region (19). The plates (2,4) are so shaped and arranged that a second by-pass area (22a) similar to the first, is defined between the second plate (4) and the first plate (2a) of an adjacent, similar, plate pair, on the inboard side of a gasket (28) clamped between the two plate pairs. A gasket groove (18) in the first plate has an inner side wall which is substantially continuous and which is of fixed or variable height substantially greater than zero.

The present invention relates to a plate type heat exchanger, and moreparticularly to an improved seal between adjacent plates in a plate typeheat exchanger. Each such pair of plates will be referred to herein as a"plate pair".

Plate type heat exchangers consist of a number of heat transfer plateswhich are clamped together in a stack in face to face relationship todefine flow channels between the adjacent :plates. Two streams of mediaeach flow through respective sets of alternate channels, the media beingin heat exchange contact through the intervening plates. The plates aresealed together at their edges and in the region of two pairs of entryand exit ports provided at the corners of the plates. A pair of portsconnects with one set of alternate flow spaces and is sealed from theother set.

Considerable attention has been paid to the seal between adjacentplates. Most typically in the past the outer edges of adjacent plates,and the region around the ports, have been sealed together by gasketswhich sit in a groove formed in one of the plates, the groove supportingthe gasket against being forced outwards by pressurised medium in theflow space. More recently, the gaskets have been replaced in whole or inpart by a permanent joint, such as adhesive, solder, braze, a plasticmould or by welding. This may be done to provide a cheaper seal or toprovide increased security against leakage of the medium from betweenthe plates.

In one prior art form of welded seal, a metal gasket is welded into agroove in a plate and is welded to the base of a corresponding groove inthe adjacent plate, that corresponding groove carrying an elastomericgasket which seals between adjacent plate pairs. Such metal gaskets areexpensive.

In another prior art form of welded seal, a pair of adjacent plates isarranged with its gasket carrying grooves back to back, the mating basesof the grooves being welded together. A thick elastomeric gasket formsthe seal between the pairs of welded plates, the gasket fitting in thefacing grooves. This mirror image arrangement results in the formationof a double gap by-pass channel which runs alongside the welded jointand provides a significantly large region of faster flow of the mediabetween the plates compared to the flow in the flow space proper,adversely affecting the performance of the heat exchanger.

According to our invention in a plate pair for a plate type heatexchanger, in which the plate pair comprises first and second platespermanently joined together at an edge region to form a seal, the firstplate is provided in the edge region with a groove facing away from thesecond plate for receiving a gasket to form a seal with a secondsimilar, adjacent, plate pair, and the underside of the groove mateswith and contacts a sealing portion of the second plate in a contactregion at which the two plates are permanently joined together to formthe plate pair with a first by-pass area defined between the platesinboard of the contact region, the groove and the sealing portion are soshaped and arranged that a second by-pass area is defined between thesecond plate and the first plate of an adjacent, similar, plate pair,and the groove has an inner side-wall which is substantially continuousand which is of fixed or variable height.

By altering the profiles of the first and second plates slightly we areable therefore to provide first by-pass area which is similar toconventional gasketted systems. Since the second by-pass area may besimilar to the first by-pass area we are able to achieve similar flowrates between the plates of a plate pair and between adjacent platepairs. This maintains the performance of a heat exchanger.

A base of the groove may mate with a planar region at the edge of thesecond plate of the pair, the planar region extending beyond the innerside wall of the groove in the first plate.

The plates are permanently sealed together by welding, brazing,soldering, plastic, or elastomeric seals.

Preferably, the base of the groove in the first plate is positionedbelow an upper boundary the plane of the second plate.

In another construction, the groove of the first plate may nest in agroove in the second plate. In such a construction the depth of thegroove in the first plate may be twice the depth of the groove in thesecond plate.

By nesting the sealing region of the plates in this manner, the by-passarea adjacent the seal can particularly be made comparable to theby-pass area in more conventional gasketed systems.

The invention will be further described by way of example with referenceto the accompanying drawings, in which:

FIG. 1 is a schematic plan view of two heat exchanger plates;

FIGS. 2, 3 and 4 are cross-sectional views of the edge region of a stackof heat exchanger plates, showing prior art systems for sealing betweenthe plates, taken generally along the line A--A of FIG. 1;

FIG. 5 is a view similar to FIGS. 2 to 4 but illustrating a firstembodiment of the invention;

FIG. 6 illustrates a second embodiment of the invention;

FIG. 7 illustrates an edge region of the plates of FIG. 6, takengenerally along the line VII--VII of FIG. 1, near a transfer port;

FIG. 8 illustrates a third embodiment of the invention; and

FIG. 9 illustrates a fourth embodiment of .the invention.

FIG. 1 shows a pair of plates 2, 4 of a plate heat exchanger. The plate2 is laid over the plate 4 and a seal is formed between the plates todefine a flow space between the plates. Plate pairs, comprising pairs ofadjacent plates, are then stacked and releasably sealed together withelastomeric gaskets, alternate flow spaces being defined between theadjacent pairs.

Each plate 2, 4 has a pattern of corrugations 6 covering a heat transfersurface 8. The corrugations of the adjacent plates bear on one anotherat respective upper and lower boundary planes (B--B) to hold the platesapart when they are compressed in a stack and to define a tortuous flowpath. Inlet and outlet holes 10, 12 provide for fluid to flow throughthe flow space between the plates 2, 4 of a pair. Through flow holes 14,16 are sealed from the flow space, and connected with the flow spaceformed between adjacent pairs of plates.

In the drawing of the first plate 2, the dash line indicates the line ofthe permanent seal between the pair of plates, whilst the chain-dot lineof the second plate 4 shows the line of the releasable gasket sealprovided between adjacent pairs of plates, the gasket being fitted tothe front face of plate 2 or the rear face of plate 4.

FIG. 2 shows a cross-section, along line A--A of FIG. 1, through a pairof plates 2, 4 and the upper plate 2a of an adjacent pair in aconventional style gasket sealing arrangement. The plates each have agroove 18 running peripherally and an elastomeric gasket 20 sits in eachgroove 18 and forms a seal between adjacent plates. Adjacent the groove18, on the side of the flow space formed between the adjacent plates, isa by-pass area 22 which presents a relatively low resistance flow pathfor the medium which flows between the plates. It is desirable tominimise this by-pass area to ensure even heating or cooling of themedium.

FIG. 3 shows a prior art system for forming a permanent seal between thepair of plates 2, 4 to form a plate pair, in which a metal gasket 24 iswelded in position to seal between the plates 2, 4. The metal gasket isused to provide, for example, enhanced resistance to corrosive fluidsand to allow for high pressure between the plates of the welded pair 2,4. The solid metal gaskets 24 are expensive.

FIG. 4 shows a gasket system as described in GB-A-2 064 750 in which thegasket groove 26 of the lower plate 4 of a plate pair is reversed, sothat the grooves 18, 26 are back to back, and a welded seam (shown bythe large dots) is formed along the bottom of the grooves 18, 26 to forma plate pair. A double height gasket 28 seals between the plates (4, 2a)of adjacent plate pairs. It can be seen that a double height by-passarea 22 (shown by hatched lines) is formed between the plates 2, 4 of awelded plate pair, no continuous by-pass area being formed between themating plates 4, 2a of adjacent pairs.

In FIG. 5, there is shown a first embodiment of the invention comprisinga pair of upper and lower plates 2 and 4 which are sealed together toform a plate pair. In the embodiment, the configuration of the upperplate 2 is conventional and similar to that in FIG. 4 with a gasketgroove 18. The inner side wall 32 of the groove 18 is formed by aninverted groove 37 which faces the lower plate 4 and forms a flowby-pass area 22. The groove 18 has an inner side-wall which issubstantially continuous and which is of fixed or variable heightsubstantially greater than zero. The lower plate 4 is largely ofconventional configuration but is not provided with a gasket groove, anda flat area 30 is formed at the edge of the plate. The flat area 30 isformed at the upper boundary plane (B--B) (as viewed in the drawing) ofthe plate 4 and extends laterally of the inner side wall 32 of thegroove 18 on the side of the flow space 31 to merge with the corrugatedheat transfer surface 8 of the plate, at a wall 33 which extends towardsthe adjacent plate 2a generally parallel to the inner wall 35 of theinverted groove 37.

The base of the gasket groove 18 is secured to the lower plate 4 at acontact region 19 to form a permanent seal. This is achieved by awelding, brazing, or soldering operation.

It can be seen that by extending the plate 4 into the boundary planeB--B opposite the groove 37 the by-pass area 22 is comparable to theby-pass area of the conventional gasketted system of FIG. 2, and similarto a second by-pass area 22a between the lower plate 4 and the adjacentplate 2a. The second by-pass area 22a is disposed inboard of and incommunication with the gasket 28 itself. In the embodiment of FIG. 5,the flat area 30 extends out to the outer edge 32a of the plate 4.

The embodiment of FIG. 6 is similar to that of FIG. 5, except a lip 34,which may be continuous or discontinuous is formed in the flat region 30on the outer edge of the plate 4, to provide greater support for thethick gasket 28.

As shown in FIG. 7, in the entry and exit zones adjacent the ports 10,12 the sealing surface of plate 4 is tapered at 33a to provide a flowgap for fluid to enter the flow space 31, and the gasket 28 between thepairs of plates is correspondingly stepped.

In the embodiment of FIG. 8, the upper plate 2 is provided with a deepgasket groove 38 which extends below the upper boundary plane B--B ofthe lower plate 4 to nest in a groove 43 in the lower plate 4. The deepgroove 38 supports a thick gasket 28' between the plates 4, 2a of theadjacent plate pairs.

It will be appreciated that the groove 43 in plate 4 may be shallower,so that the groove 38 need only extend a short distance below themid-plane B--B, the preferred extremes of the range of depth of thegasket groove being illustrated by the embodiments of FIG. 5 and 8.Also, the outer wall 39 of the groove 43 need not be provided. Forexample, the plate 4 may extend outwards (to the left in the drawing) inthe plane of base of groove 43, and it may extend upwards near its outeredge to meet the outer edge of the plate 2.

The inner wall 41 of the groove 43 extends upwards towards the firstplate 2 to reduce the by-pass area 22.

The deep groove 38 is preferably stepped up to the level of themid-plane B--B in the region of the entry and exit ports 10, 12. Thecooperating groove and the gasket in this region being stepped also.

In the embodiment of FIG. 9, the base of the groove 43' in the lowerplate 4 is stepped upwards so as to lay at about half the plate heightand a step 40 is provided in the sidewalls 42 of the deep upper groove38', which is about 1.1/2 plate heights deep. The contact region 19comprises the engagement between the lower face of the groove 38' andthe upwards step in the lower plate 4. The inner wall 41' of the groove43' extends upwardly towards the upper plate 2 to reduce the by-passflow area 22.

In each plate pair described above with reference to FIGS. 5-9, each ofthe two plates may be constructed from the same material, or fromdifferent materials.

Each of the two plates 2, 4, 2a, 4a of each plate pair may also comprisetwo or more layers of sheet material which rest into each other. Thelayers may be constructed from the same material, or from differentmaterials.

We claim:
 1. A plate pair for a plate type heat exchanger, said platepair comprising first and second plates, said first and second plateseach having an edge region, said first and second plates beingpermanently joined together at said edge region to form a seal at acontacting region, in which said first plate defines in said edge regiona groove, said groove facing away from said second plate, said groovereceiving a gasket to form a further seal with a second similar,adjacent, plate pair, said groove having an underside, said underside ofsaid groove mating with and contacting a sealing portion of said secondplate in said contact region, said first and second plates inboard ofsaid contact region defining a first by-pass area, said groove, saidsealing portion, said second plate and said first plate of an adjacent,similar, plate pair, being so shaped and arranged as to define a secondby-pass area, said groove defining an inner side-wall, said side-wallbeing substantially continuous and being fixed or variable in height. 2.A plate pair according to claim 1, in which said second plate has aregion adjacent said contact region on the side of the said by-passarea, said region extending towards said first plate.
 3. A plate pairaccording to claim 2, in which said base of said groove in said firstplate is positioned below an upper boundary plane of said second plate.4. A plate pair according to claim 1, in which said groove has a base,said edge of said second plate of said pair having a planar region, saidbase mating with said planar region, said planar region extending beyondthe inner side wall of said groove in said first plate.
 5. A plate pairaccording to claim 4, in which said planar region is formed in an upperboundary plane of said second plate.
 6. A plate pair according to claim5, in which said inner edge of said planar region is terminated by awall, said wall extending away from said first plate towards a firstplate of an adjacent plate pair.
 7. A plate pair according to claim 6,having entry and exit ports, in which, in the vicinity of said entry andexit ports, said wall is formed closer to said contact region.
 8. Aplate pair according to claim 1, in which said groove of said firstplate nests in a groove in said second plate.
 9. A plate pair accordingto claim 8, in which the depth of said groove in said first plate istwice the depth of said groove in said second plate.
 10. A plate pairaccording to claim 8, in which said groove in said second plate definesan inverted portion, said inverted portion being of a height less thanthe maximum depth of said groove in said second plate and said groove insaid first plate is, for at least part of its width, twice said maximumdepth of said groove in said second plate less the height of saidinverted portion of said groove of said second plate, said contactregion comprising the lowest base of said first plate and the uppersurface of said inverted portion of said second plate.
 11. A plate pairaccording to claim 1, in which said inner edge of said planar region iscontiguous with a heat exchanging portion of said second plate.
 12. Aplate pair according to claim 1, in which each plate comprises a plateelement, said plate element being constructed from at least two layersof sheet material, said layers nesting into each other.
 13. A plate pairaccording to claim 12, in which said layers are constructed from thesame material.
 14. A plate pair according to claim 12, in which said twolayers are constructed from different materials.
 15. A plate pairaccording to claim 1, in which said two plates are joined together atsaid contact region by a permanent joint comprising welding, soldering,or brazing.
 16. A heat exchanger of the multi-plate type comprisingadjacent plate pairs of which the plates of each pair are permanentlysealed together, and gaskets disposed between adjacent plates ofadjacent plate pairs form seals, each of said plate pair comprisingfirst and second plates, said first and second plates each having anedge region, said first and second plates being permanently joinedtogether at said edge region to form a seal at a contacting region, inwhich said first plate defines in said edge region a groove, said groovefacing away from said second plate, said groove receiving a gasket toform a further seal with a second similar, adjacent, plate pair, saidgroove having an underside, said underside of said groove mating withand contacting a sealing portion of said second plate in said contactregion, said first and second plates inboard of said contact regiondefining a first by-pass area, said groove, said sealing portion, saidsecond plate and said first plate of an adjacent, similar, plate pair,being so shaped and arranged as to define a second by-pass area, saidgroove defining an inner side-wall, said side-wall being substantiallycontinuous and being fixed or variable in height.
 17. A plate pairaccording to claim 16, in which said second plate has a region adjacentsaid contact region on the side of the said by-pass area, said regionextending towards said first plate.
 18. A plate pair according to claim17, in which said base of said groove in said first plate is positionedbelow an upper boundary plane of said second plate.
 19. A plate pairaccording to claim 16, in which said groove has a base, said edge ofsaid second plate of said pair having a planar region, said base matingwith said planar region, said planar region extending beyond the innerside wall of said groove in said first plate.
 20. A plate pair accordingto claim 19, in which said planar region is formed in an upper boundaryplane of said second plate.
 21. A plate pair according to claim 20, inwhich said inner edge of said planar region is terminated by a wall,said wall extending away from said first plate towards a first plate ofan adjacent plate pair.
 22. A plate pair according to claim 21, havingentry and exit ports, in which, in the vicinity of said entry and exitports, said wall is formed closer to said contact region.
 23. A platepair according to claim 17, in which said groove of said first platenests in a groove in said second plate.
 24. A plate pair according toclaim 23, in which the depth of said groove in said first plate is twicethe depth of said groove in said second plate.
 25. A plate pairaccording to claim 23, in which said groove in said second plate definesan inverted portion, said inverted portion being of a height less thanthe maximum depth of said groove in said second plate and said groove insaid first plate is, for at least part of its width, twice said maximumdepth of said groove in said second plate less the height of saidinverted portion of said groove of said second plate, said contactregion comprising the lowest base of said first plate and the uppersurface of said inverted portion of said second plate.
 26. A plate pairaccording to claim 16, in which said inner edge of said planar region iscontiguous with a heat exchanging portion of said second plate.
 27. Aplate pair according to claim 16, in which each plate comprises a plateelement, said plate element being constructed from at least two layersof sheet material, said layers nesting into each other.
 28. A plate pairaccording to claim 27, in which said layers are constructed from thesame material.
 29. A plate pair according to claim 27, in which said twolayers are constructed from different materials.
 30. A plate pairaccording to claim 16, in which said two plates are joined together atsaid contact region by a permanent joint comprising welding, soldering,or brazing.